Alluvial Fan Deposits Research Articles

Alluvial fan, braided river and shallow-marine turbidity current deposits in the Port Lazo and Roche Jagu formations, Northern Brittany: relationships to andesite emplacements and implications for age of the Plourivo-Plouézec Group

AbstractFacies and stratigraphic analysis of the Port Lazo and Roche Jagu formations, together the lower part of the Plourivo-Plouézec Group, suggests deposition in three distinct depositional systems. The lower part of the Port Lazo Formation comprises red conglomerate, sandstone and shale of alluvial fan to alluvial plain origin. A conformable interval of grey sandstone and shale succeeds the lower Port Lazo red beds and records a period of subtidal sedimentation dominated by river-fed, shallow-water turbidity currents (hyperpycnites). The succeeding Roche Jagu Formation comprises red sandstones and shales of braided fluvial origin. It is intercalated with, and succeeded by, andesites. The andesites succeeding the fluvial strata overlie a prominent erosion surface and are lava flows, whereas those intercalated with the fluvial strata are intrusions. Rb–Sr radiometric dating of the andesites at 472+/−5 Ma is commonly used as evidence for the whole Plourivo-Plouézec Group being Early Ordovician in age. However, the stratigraphic relationships and patterns of sedimentation in the Port Lazo and Roche Jagu formations, together with the localized presence ofArumberia, suggest they are most likely of early Cambrian age and related to a phase of post-Cadomian rifting. The facies deposited show both similarities to and differences from neighbouring strata of equivalent age, and highlight the control exerted by sediment load on alluvial and nearshore processes on early Palaeozoic environments.

The Liuqu Conglomerate, southern Tibet: Early Miocene basin development related to deformation within the Great Counter Thrust system

The Liuqu basin formed during the early Miocene between ophiolitic melanges (to the south) and uplifted Cretaceous forearc deposits (to the north) along a central, 150-km-long segment of the India-Asia suture zone in southern Tibet. Sedimentological analysis shows the Liuqu Conglomerate to be composed of mixed fluvial and sediment-gravity flow lithofacies assemblages locally interbedded with mature paleosols. We interpret the Liuqu Conglomerate as coarse-grained fluvial and alluvial-fan deposits. Structural analysis indicates that the Liuqu Conglomerate was deposited in a contractional setting. Paleocurrent and provenance data demonstrate that sediment was transported north-northwest from the hanging wall of a coeval thrust fault system along the southern limit of Liuqu outcrops. Detrital zircon U-Pb ages (and Hf[ t ] isotope ratios) cluster around 80–110 Ma (eHf[t] = −23.5–14.6), 120–135 Ma (eHf[t] = −12.6–13.1), 150–170 Ma (eHf[t] = −14.1–14.7), 500–600 Ma (eHf[t] = −26–3.4), and 1100–1200 Ma (eHf[t] = −27.6–2.9), requiring input from both Gangdese and melange sources. Asian zircons were recycled northward after being incorporated into accretionary melanges along the southern Asian margin prior to India-Asia collision. The age of the Liuqu Conglomerate is still somewhat uncertain, but new chronologic data, including biotite 40Ar/39Ar data, detrital zircon fission-track analyses, and δ13C compositions of soil carbonates, all converge on ca. 20–19 Ma as the most probable age. Together, these results indicate that part of the north-to-south sediment transport system that existed prior to India-Asia collision and into the Eocene was reversed by ca. 20 Ma. The Liuqu Conglomerate may represent deposits associated with the paleo–Yarlung River.

Restoration of the external Scandinavian Caledonides

AbstractThree models are evaluated for restoring basement rocks coring tectonic windows (Window-Basement) in the Scandinavian Caledonides; parautochthonous (Model I) and allochthonous (models II/III), with initial imbrication of the Window-Basement post-dating or pre-dating, respectively, that in the external imbricate zone (Lower Allochthon). In Model I, the Window-Basement comes from the eastern margin of the basin now imbricated into the Lower Allochthon, while in models II/III it comes from the western margin. In Model II, the Window-Basement formed a basement-high between Tonian and Cryogenian sediments imbricated into the Middle and Lower allochthons; in Model III deposition of the Lower Allochthon sediments commenced in Ediacaran times. Balanced cross-sections and branch-line restorations of four transects (Finnmark–Troms, Västerbotten–Nordland, Jämtland–Trøndelag, Telemark–Møre og Romsdal) show similar restored lengths for the models in two transects and longer restorations for models II/III in the other transects. Model I can result inc.280 km wide gaps in the restored Lower Allochthon, evidence for which is not seen in the sedimentology. The presence of <3 km thick alluvial-fan deposits at the base of the Middle Allochthon indicates proximal, rapidly uplifting basement during Tonian–Cryogenian periods, taken as the origin of the Window-Basement during thrusting in models II/III. Model I requires multiple changes in thrusting-direction and predicts major thrusts or back-thrusts, currently unrecognized, separating parts of the Lower Allochthon; neither are required in models II/III. Metamorphic data are consistent with models II/III. Despite considerable along-strike structural variability in the external Scandinavian Caledonides, models II/III are preferred for the restoration of the Window-Basement.

Subsurface constraints of an active detachment fault in Laguna Salada Basin, Baja California, México, from interpretation of seismic-reflection profiles

The Laguna Salada Basin in northeastern Baja California, Mexico, is an active half-graben with subsidence principally controlled by two major faults along the eastern basin margin—the Canada David detachment fault and the dextral oblique Laguna Salada fault. Active-source, seismic-reflection data constrain the geometry of the active detachment fault and indicate two structural domains. The south domain is a supradetachment basin controlled by the Canada David detachment fault. Two seismic profiles indicate the detachment fault dips 17°–20° west, has a minimum of 10.1 km of slip, and accumulates a sedimentary wedge more than 2.5 km thick in the west-central part of this basin domain. This estimation indicates that the subsurface portion of the Canada David detachment accommodates 24% of extension in the western main plate boundary zone. The north domain is a dilatational stepover (or pull apart) controlled by the northwest-trending, west-dipping, dextral-oblique Laguna Salada fault and the north-trending, dip-slip Canon Rojo fault, which defines the south boundary of the pull-apart basin domain. The Canon Rojo fault accumulates more than 2 km of subsidence, but geometric considerations indicate that the basement in the hanging wall of the Laguna Salada fault projects to a depth of ∼3.8 km and intersects the 70° west-dipping Laguna Salada fault. Several faults cut the west margin of the floodplain lagoon and the hanging wall of both the Canada David detachment and the Laguna Salada fault. The largest fault is west dipping and produces ∼500 m of vertical offset. Its location projects south of the Canon Rojo fault, and we speculate these two faults may correlate. Seismic facies reflect its sedimentary environment and processes. Seismic facies 1 is high-amplitude, laterally continuous reflectors that represent flooding and prolonged lacustrine conditions. Seismic facies 2 is high- to low-amplitude, laterally discontinuous reflectors also representing flooding conditions. Seismic facies 3 is low-amplitude, poorly contrasted continuous to discontinuous reflectors interpreted as subaerial distal fan sandstone deposits. Seismic facies 4 is high-amplitude, discontinuous, imbricated to a chaotic pattern of reflectors. We interpret facies 4 as coarse-grained, high-energy alluvial fan deposits prograding over the basin floor from the west in the range front of Sierra Juarez. Seismic facies 1 and 2 predominate in the east and central portions of seismic profiles where the depocenter accumulates thicker sedimentary sequences.

Reconstruction of Late Quaternary climate and seismicity using fluvial landforms in Pindar River valley, Central Himalaya, Uttarakhand, India

Fluvial landforms in the Pindar River valley are investigated to understand the role of temporal variability in the Indian Summer Monsoon (ISM) and the spatial changes in crustal deformation. Employing the conventional geomorphological and sedimentological concepts, supported by optical dating, three major phases of valley-fill aggradation separated by phases on non-deposition are discerned. An oldest aggradation phase is dated to 33.5 ka during relatively strengthened ISM corresponding to the later part of pluvial Marine Isotopic Stage-3 (MIS-3). Following this, alluvial fan sedimentation impersistently continued during the declining phase of the ISM (until around 21 ka). A second major aggradation phase (17.5 ka–13 ka) occurred during the post-LGM/lateglacial strengthening of the ISM in which contribution from tributary valleys overwhelmed the valley-fill sedimentation. A youngest aggradation phase dated to the middle to late-Holocene (8 ka–3.6 ka), represents the transitional climate during which sporadic high sediment fluxes both from the upper catchment and tributary streams led to the development of fossil valleys (abandonment of old channels).The spatial variability in the incision/uplift rate, based on river strath terraces reveals that the terrain is undergoing differential crustal deformation. Two zones of relatively high crustal deformation are identified. These are located in the vicinity of the Main Central Thrust (MCT) and is attributed to the activity along the transverse fault and the in the inner Lesser Himalaya for which the thrust propagated fold associated with regional north-south compression is implicated. The study suggests that fluvial landforms (valley-fill and strath terraces) in the Pinder river valley are genetically related to the multi-millennial scale changes in the ISM and spatial and temporal changes in the crustal deformation associated with regional compression.

The Stebnyk Formation (Miocene) in the Boryslav-Pokuttya and Sambir nappes of the Ukrainian Carpathians: a record of environmental change in the Carpathian Foredeep

The late Early–Middle Miocene Stebnyk Formation is a ~600–2000 m thick unit of the Boryslav-Pokuttya and Sambir nappes, which contains a molasse succession of the Carpathian Foredeep incorporated within the marginal part of the Outer Eastern Carpathian accretionary wedge. In the valley of thePrutRiver, between Deliatyn and Lanchyn, the Stebnyk Formation covers the alluvial fan deposits of the Sloboda Conglomerate and the deltaic deposits of the Dobrotiv Formation in the south, and the lagoonal salty clays of the Vorotyscha Formation in the north. The Stebnyk Formation is built of mainly rose, greenish and grey calcareous mudstones intercalated with several variable sandstone beds, including thick-bedded packages. The occurrence of tetrapod footprints and raindrop imprints, as well as the overall red-be character prove prevailing continental conditions during deposition of the formation, which is interpreted as sediments of a delta plain with distributary channels filled by the thick sandstone beds and associated by intercalations of thinner beds referred to channel levees and crevasse splays. The upper part of the Stebnyk Formation contains marine microfossils of the NN4 Zone, and locally to the NN5 Zone, corresponding to the early Badenian transgression in the region. In the regional scale, the Stebnyk Formation shows a polarity of facies, with a high contribution of conglomerates and thick-bedded sandstones in the lower part in the north west and fining to the south east, with transportation from the west and north west. The sediments accumulated in an elongated subsiding zone between the rising Carpathian orogen and the forebulge elevation of the foreland, in a warm and semi-dry climatic conditions corresponding roughly to the Mid-Miocene Climatic Optimum. The accumulation was balanced by a subsidence caused by sinking of the platform slab and by sedimentary load.

Oyster Shells As Recorders of Short-Term Oscillations of Salinity and Temperature During Deposition of Coral Bioherms and Reefs In the Miocene Lorca Basin, SE Spain

Abstract: We use δ 18 O and δ 13 C of oyster shells, inferred seawater δ 18 O (δ w ), and temperature tolerance ranges of modern zooxanthellate coral communities to constrain and model paleo-salinities of marginal-marine waters of the Miocene Lorca Basin, Spain. Salinities ranged from 22 to 32 PSU during growth of coral bioherms and carpets of the Soriana and Parrilla formations, and from 35 to 39 PSU during deposition of the Hondo Formation reef complex. The periods with lower modeled salinities correspond with deltaic and alluvial-fan sedimentation in the area. The modeling is supported by 87 Sr/ 86 Sr data and provides new insights into the evolution of the local depositional settings. Departures of Sr-isotope values from the global oceanic curve occur within the intervals with the lowest modeled salinities, and the non-oceanic 87 Sr/ 86 Sr preserved in individual oyster shells was probably sourced from uplifted Aquitanian–Burdigalian limestones. 87 Sr/ 86 Sr values that plot along the global ocean Sr-isotope curve for the late Miocene indicate a Tortonian age for the upper part of the Soriana Formation and the Parrilla Formation, and a Messinian age for the Hondo Formation. More generally, we demonstrate how the chemical analyses of oyster shells provide additional information regarding short-term oscillations of salinity and temperature of seawater beyond what can be obtained by traditional paleoecological methods.

Constraints on synrift intrabasinal horst development from alluvial fan and aeolian deposits (Triassic, Fundy Basin, Nova Scotia)

Abstract The Triassic Fundy rift basin in Nova Scotia is a large (>70 km wide) half-graben filled with alluvial, lacustrine and aeolian deposits. A major lithospheric lineament, the Cobequid–Chedabucto Fault Zone (CCFZ), which forms the tip of the Newfoundland–Gibraltar Fault Zone, occurs within the Fundy Basin. The timing of early movement on this important fault zone is poorly constrained. We present data from the alluvial and aeolian units that crop out adjacent to the CCFZ in the Minas sub-basin to determine the initiation of fault movement. We use the onset of alluvial fan deposition to infer when the fault became sufficiently active to create the intrabasinal topography and document the influence of fault activity on the intrabasinal drainage. The occurrence and preservation of aeolian deposits immediately adjacent to the CCFZ and concomitant with alluvial fan development suggests a wind shadow effect associated with the fault-generated topography. The onset of alluvial fan deposition associated directly with the fault occurred during Norian times, following an earlier phase of sedimentation in the Fundy Basin, and records a potentially important phase of plate reorganization during early Atlantic rifting.

The fossil beach and reef terraces of the Gulf of Aqaba coast, Jordan—its environment, formation, and relation to mountain uplifting mechanism

In the southern part of the eastern Jordanian coast of Aqaba Gulf at least three raised fossil reefs were mapped. These fossil reefs were deposited on alluvial fan deposits and are laterally connected with clastic shore sediments simultaneously deposited with their corresponding reef. The highest mapped fossil reef lies at an elevation of about 75 m above present sea level, the other two lie at lower elevations of around 60 m above sea level and 20 m above sea level. Geological and paleontological evaluation places the highest reef as the most recent fossil reef. Sea level had been following the rises and falls caused by subsequent glacial growths and the sea, since about 20,000 years, has only been rising. The alluvial material into and onto which the beech, lagoon, and reefs had been deposited during or before the time of the Eemian Interglacial and it had become detached from its source area during or subsequent the moist time of the last interglacial period. It is assumed by previous studies that the reefs are still younger than 200,000 years, and in that case the rise of the fossil reefs is due to taphrogenic and epirogenic movements and has not been caused by eustatic fluctuations. Such movements have affected the Gulf of Aqaba and the Jordan Rift Valley since Oligocene times.

Lithological control of land subsidence induced by groundwater withdrawal in new urban AREAS (Granada Basin, SE Spain). Multiband DInSAR monitoring

AbstractGround subsidence in the southeastern border of the Granada Basin (SE Spain) has been studied using remote sensing techniques. Over the last decades, the region has experienced a huge urban expansion, which has caused a substantial increase in water supply requirements. Water needs are exclusively met by groundwater by means of numerous pumping wells, which exploit a confined detrital aquifer of alluvial fan deposits with a heterogeneous facies distribution. A general piezometric level decline (up to 50 m) has been recorded in the aquifer during the past 30 years that has induced the generation of a subsiding area with oval shape oriented WNW‐ESE just where the new urban areas and pumping wells are located. Subsidence has been monitored by exploiting synthetic aperture radar (SAR) images from ENVISAT (2003–2009) and Cosmo‐SkyMed (2011–2014). A new approach, which combines A‐DInSAR and small‐area persistent scatterer interferometry (PSI) analysis, has been applied obtaining a good accuracy regarding temporal and spatial dimension of the subsidence. ENVISAT data (2003–2009) reveal subsidence rates up to 10–15 mm/year, and Cosmo‐SkyMed (2011–2014) values slightly lower; up to 10 mm/year. Temporal variations in the subsidence velocity are in accordance with the rainfall pattern and piezometric fluctuations in the aquifer. The sector with highest rates of subsidence does not correspond to the area with more intense groundwater exploitation but to the area with greater presence of clays in the confining layer of the aquifer. There is a clear lithological control in the spatial distribution of the ground subsidence. This work integrates detailed geological and hydrogeological data with differential SAR interferometry monitoring with the aim to better understand subsidence processes in detrital aquifers with small‐scale heterogeneity. Copyright © 2016 John Wiley & Sons, Ltd.

Neogene-Quaternary evolution of the Tefenni basin on the Fethiye-Burdur fault zone, SW Anatolia-Turkey

The Fethiye-Burdur fault zone (FBFZ) is a complex belt of major break in the southwestern Anatolia. A number of basins occur within the FBFZ. The Tefenni basin is one of the NE-SW trending basins located in the central part of the FBFZ. The basin is 10–20 km wide and 60 km long. It contains two infills of fluvial, lacustrine and alluvial fan deposits from late Miocene to Recent. The older and folded infill rests on the pre-middle Miocene basement rocks with an angular unconformity and consists of fluvial and lacustrine sediments. The younger and undeformed Plio-Quaternary basin fill unconformably overlies the older basin fill and is composed predominantly of conglomerate, mudstone, silt, clay and recent basin floor sediments. The Tefenni basin is controlled by a series of NE-SW trending left lateral oblique-slip normal faults along its margins. The Tefenni and Mürseller faults bound the northwestern margin of the basin and the Kemer fault bounds the southeastern margin of the basin. The basin is also cut by NE-SW striking major and NW-SE, N-S and E-W striking small scale normal faults. Structural analyses in the basin show that NE-SW-trending contraction stress regime ended by Pliocene and was followed by NE-SW-trending extension from Pliocene onward.

At the Intersection of Geology, Archaeology, History, and Art: Engineer Cantonment (1819–1820), Washington County, Nebraska

In the fall of 1819, members of the Stephen Long Expedition constructed two log and limestone buildings along the west bank of the Missouri River north of modern Omaha, Nebraska, to serve as their winter quarters (Engineer Cantonment). A detailed watercolor and sketches of the site by expedition member Titian Ramsay Peale were key to the rediscovery of Engineer Cantonment. Subsequent excavations of the site identified three distinct archaeological components: two Native American hearths that date to the late Holocene, about 870 and 810 14 C years before present (BP), the Engineer Cantonment from AD 1819–20, and a farmstead from the late 19th to mid-20th century. The site is a low terrace-fan complex composed of four major depositional units: a late Holocene Missouri River alluvial fill, a late Holocene through modern alluvial fan, a younger historic alluvial fill, and 19th-to 20th-century Missouri River floodplain deposits. The late Holocene fill is a fining-upward sequence of channel sand and gravel overlain by silt and clay overbank deposits with redoximorphic features. The fan includes multiple beds of yellowish brown, brown, and gray alluvial fan sediments with thin, weakly developed buried soils. The historic alluvial fill truncates the distal portions of the alluvial fan and the upper portions of the late Holocene fill. The modern floodplain deposits consist of a thin bed of silty clay overlying cross-bedded silty sand. Our study demonstrates two things: the significance of the margins of the valley floor of the Missouri River as a record of late Pleistocene through modern fluvial activity, and a potentially long record of human occupation of the valley during the Holocene. This project also demonstrates the potential usefulness of 19th-century art in the study of cultural and environmental change during the last two centuries.

Morphodynamics and facies architecture of streamflow-dominated, sand-rich alluvial fans, Pleistocene Upper Valdarno Basin, Italy

Abstract The overwhelming documentation of coarse-grained alluvial fans dominated by mass flow contrasts with the scarce accounts of finer grained, traction-dominated alluvial fans. To fill this gap, we present sedimentological and architectural data from a set of sand-rich, streamflow-dominated Pleistocene fans flanking the eastern Upper Valdarno Basin, Italy. The routing of sand-rich sediment resulted from the fast, intense weathering of the feldspar-rich, carbonate-deprived sandstone bedrock underlying the fan catchments. Although capable of entraining large boulders, high water discharge sustained tractional reworking along the proximal facies belts, hindering mass flow. The medial facies belts have a channelized, braided planform and are dominated by processes hardly distinguishable from those characterizing fluvial environments. Along the distal facies belts, extensive overbank tracts are composed of terminal splays and crevasse lobes, the spatial arrangement of which controlled the evolution of through-going tributary channels connected to the axial basin drainage. This study focused on the sedimentary processes, stratal architecture and morphodynamics of the alluvial fans and considered the effect of bedrock inheritance on their development. The results underline how granulometry and mass flow dominance are not distinctive of alluvial fan sedimentation per se and indicate how the critical detection of piedmont, radial palaeomorphology is crucial in the identification of ancient alluvial fans.

Spatial characteristics of the Pliocene to modern alluvial fan successions in the uplifted sedimentary basins of Almería, SE Spain: review and regional synthesis

Abstract Conventional sedimentological models of alluvial fan sequences tend to be based on fans in subsiding sedimentary basins. Fans in uplifting terrains are rather different. We examined the sequence of fan delta and alluvial fan deposition from the Pliocene to the Late Quaternary in the uplifting terrain of the Neogene sedimentary basins of Almería, Betic Cordillera, SE Spain. There were three phases of fan deposition, each yielding particular morpho-sedimentological characteristics and each having distinctive spatial distributions. The first phase was the Pliocene fan deltas, deposited where the larger river systems entered the receding early Pliocene seas. This phase was followed during the late Pliocene–Early Pleistocene by a phase of extensive alluvial fan deposition extending from the mountain fronts to the basin centres. Continued uplift occurred during the Pleistocene, resulting in incision of the drainage network and dissection of the Plio-Pleistocene fan systems. The third phase, during the Quaternary, involved much smaller mountain front alluvial fans set well below the Plio-Pleistocene fans, except in local areas of tectonic subsidence where extensive fans were formed. The older fans exhibit stacked sedimentary successions with very little evidence of sustained vertical incision. However, the Quaternary fans show much evidence of sustained incision between major aggradational phases, often resulting in inset rather than stacked stratigraphic relationships. We interpret this to imply that, although the tectonic context was the primary temporal control on variations within the older fan successions, within the Quaternary fans the overall tectonic control has been modified by responses to the Quaternary climatic sequence.

Early non-marine life: Evaluating the biogenicity of Mesoproterozoic fluvial-lacustrine stromatolites

The record of life on land or in non-marine environments during the Precambrian is sparse, limiting our ability to understand life outside of marine settings before the advent of animals. Stromatolites from such environments are known, but demonstrating stromatolite biogenicity remains difficult, as stromatolite growth can be controlled by a spectrum of biologic, chemical, and biologically-mediated processes. Stromatolites from the Mesoproterozoic (1.09 Ga) Copper Harbor Conglomerate, an alluvial fan, fluvial, and lacustrine deposit, offer an interesting test for the presence and nature of microbial life in shallow, Mesoproterozoic non-marine settings.Stromatolites from a siltstone facies are interpreted as biogenic, as they contain detrital-rich laminae, likely indicative of trapping and binding by microbes and fenestral fabrics suggestive of desiccation or lift-off structures in mats via the presence of gas (perhaps O2 from photosynthesis or other gases from mat decay). The stromatolites formed as microbial mats grew over a mudflat or sandflat with carbonate filled desiccation cracks on an erosive topography, and thus provide evidence for life in a very shallow, predominantly desiccated environment. Stromatolites from a conglomerate facies are microdigitate and record both isopachous laminae with radial-fibrous calcite fans and botryoids, typically considered abiogenic in origin, as well as wavy, conical laminations likely indicative of the former presence of microbial mats. The conglomerate-facies stromatolites are interpreted to have formed in a flooded braidplain setting with restricted circulation. This study supports the suggestion that microbial communities were abundant in non-marine environments in the Midcontinent Rift during the Mesoproterozoic. It also highlights how variable environmental factors can influence stromatolite growth, even in similar depositional settings and with a consistent microbial presence.

Neoproterozoic stratigraphy of the Zavkhan terrane of Mongolia: The backbone for Cryogenian and early Ediacaran chemostratigraphic records

The Neoproterozoic Tsagaan-Olom Group is exposed in the Zavkhan Terrane of southwestern Mongolia and hosts unique geochemical, paleoclimate, and paleontological records that have become central to our understanding of this pivotal interval of Earth history. New sedimentological, stratigraphic, geochronological, and geochemical data provide context for and further develop these records. Detrital zircon provenance indicates that Neoproterozoic strata of the Zavkhan Terrane were derived from basement with age peaks between 1950 to 2100 and 2400 to 2600 Ma. At ∼800 Ma, the Zavkhan Terrane transformed from an active arc and back-arc complex to a rifted ribbon continent with passive margins on both sides. Deposition was accommodated by extension, which is recorded with syn-sedimentary normal faulting and alluvial fan deposition in the Zavkhan and Khasagt formations. Passive margin sedimentation in the overlying Tsagaan-Olom Group begins with the glacigenic Maikhan-Uul Formation, which consists of two massive diamictite units separated by clast-poor graded beds of the middle member. Detrital zircon at the base of the middle member of the Maikhan-Uul Formation were dated with U-Pb chemical abrasion isotope-dilution thermal ionization mass spectrometry and constrained its age to

Stratigraphy and fossil plants from the Cutler Formation (Late Paleozoic) and their paleoclimatic implications, eastern Paradox Basin, Colorado

Exposures of the late Paleozoic Cutler Formation, near the town of Gateway, Colorado, have traditionally been interpreted as the product of alluvial-fan deposition along the western flank of the Uncompahgre uplift and within the easternmost portion of the Paradox Basin. The Paradox Basin formed between the western margin of the Uncompahgre uplift, a segment of the Ancestral Rocky Mountains, and the western paleoshoreline of the North American portion of Pangea. This part of Pangea is commonly thought to have experienced semi-arid to arid conditions and warm temperatures during the Pennsylvanian and Permian. We present stratigraphic and fossil plant evidence in this paper to support prior interpretations that the Cutler near Gateway, Colorado, was deposited by alluvial fans that hosted localized wetland areas. Our findings are consistent with the results of prior studies that have suggested the climate in the area was warm, semi-arid, and ice-free at the time the plants described in this paper were living. 
 Plant fossils collected from the Cutler Formation came from two sites in The Palisade Wilderness Study Area (managed by the U.S. Department of the Interior, Bureau of Land Management) of western Colorado. The stratigraphic sections at the sites were composed mostly of pebble to cobble conglomerate and sandstone, but the fossil plants were mainly preserved in fine-grained intervals (fine-grained sandstone to siltstone). The preservation of plant fossils in the proximal Cutler Formation is remarkable because the surrounding sections consist mostly of conglomerate and sandstone interpreted as fluvial and debris-flow deposits. The fine-grained strata containing the plant horizons must have been deposited in a wet and protected setting, possibly a spring-fed abandoned channel on the alluvial fan. The plants and their surrounding sediment must have been rapidly buried in order to allow for long-term preservation of the fossils. It seems likely that vegetation was abundant in and adjacent to low-lying wet areas on the fan’s surface, based on the abundance of plant fossils found at the two sites. The fossil plant assemblage includes Calamites, Walchia, and Pecopteris. The flora are interpreted to have lived near the apex of the alluvial-fan system. These fossils suggest that warm and at least seasonally and locally wet conditions existed in the area during the time that the plants were growing. More arid conditions during the late Paleozoic are suggested by the characteristics of some of the time-equivalent and near time-equivalent rocks exposed to the west of the study area in the central Paradox Basin.

A Reinterpretation of the Baturetno Formation: Stratigraphic Study of the Baturetno Basin, Wonogiri, Central Java

DOI:10.17014/ijog.2.3.125-137This paper focuses on the Quaternary Baturetno Formation. An earlier research concluded that the black clay of the Baturetno Formation formed as a ‘palaeolake’ deposit. The ‘palaeolake’ was interpreted to form due to the shifting course of the Bengawan Solo Purba River in relation to Pliocene tectonic tilting in the southern Java. The stratigraphy of the Baturetno Formation was observed in the western part of the Baturetno Basin, and based on marker beds, the Baturetno Formation was classified into three units: (1) Gravel unit (GR) in the upper part, (2) clay unit (CU) in the middle part, and (3) sand-gravel unit (SG) in the lower part. There are floating gravel fragments of andesite, claystone, coral, and limestone with diameters of up to 10 cm in the clay unit. The particle size of sediment reflects the environment, but the lake deposition occurs under very quiet conditions. The occurrence of these fragments within the clay cannot be explained if the clay was deposited within a lake environment. The occurrence of floating fragments in the black clay of Baturetno Formation can best be explained through mudflow process. The cohesive strength of the mudflow is responsible for the ability of large fragments to float within the mud matrix. In general, the Baturetno Formation is inferred to be an alluvial fan deposit. The presence of sand, gravel, and mud are characteristics of alluvial fan deposits.

The Upper Jurassic–Lower Cretaceous alluvial-fan deposits of the Kalaza Formation (Central Asia): tectonic pulse or increased aridity?

Abstract The topographical evolution of tectonic systems, as well as the sedimentation pattern and depositional environments in the associated basins, are controlled by both tectonics and climate. In the region of the Tien Shan (Central Asia), the Jurassic–Lower Cretaceous period was marked by complex, low-intensity tectonic deformation and major climate changes from humid to arid conditions (Jurassic) to semi-arid conditions (Cretaceous). Using the sediment record in the Junggar, Tarim and Fergana basins to describe the tectonic evolution of the Tien Shan area during the Mesozoic thus requires differentiation between the tectonic and climatic influences on sedimentation. The conglomerates of the Upper Jurassic–Lower Cretaceous Kalaza Formation were commonly associated with renewed tectonic activity resulting from the docking of the Lhasa block along the southern margin of Asia. From sedimentology and sequence stratigraphy analyses of several sections in the Junggar, Tarim and Fergana basins, we reassess the main factors controlling the deposition of this formation. We show that, while some tectonic activity persisted throughout the Jurassic–Cretaceous transition, the switch from the sandy deposits of the Upper Jurassic Qigu Formation to the coarse deposits of the Kalaza Formation is largely linked to the development of an arid climate.

Analysis of geomorphic indices in the southern Central Andes (23°–28°S): Evidence for pervasive Quaternary to Recent deformation in the Puna Plateau

Satellite data-based morphotectonic analyses are popular methods to identify active crustal deformation of large and partly remote regions, such as the Central Andes. For the southern Central Andes between 23° to 28°S, the mountain-front sinuosity (Smf-) index was estimated for 189 first-order mountain fronts, as well as valley shape (Vf-) ratios and basin symmetry (T-) factors for 3366 second-order, tributary drainage basins. The correlation between known fault ages and Smf-indices shows that the indices can be used as a proxy to infer the ages of faults for which radiometric ages do not exist. Vf-ratios and Smf-indices point to pronounced Quaternary to Recent surface deformation on first-order reverse faults delimiting mountain fronts. By contrast, analysis of the transverse topographic symmetry (T-) factor, which has been used to assess rotational components of drainage basins, points to stochastic variations of erosion, possibly due to local lithological heterogeneity, rather than to a tectonic influence on basin geometry. We also examined 32 mainly NNE-SSW trending first-order basin margins for tilt of alluvial fan deposits and lateral stream migration. The symmetry of first-order basins in the southern Central Andes seems to be strongly controlled by Quaternary deformation on bivergent first-order reverse or thrust faults. Quaternary deformation of the upper crust in the Puna Plateau is apparently more pervasive than previously appreciated and has important ramifications for the Neogene to Recent morphotectonic evolution of the southern Central Andes.